Hunting bullet with reduced aerodynamic resistance

ABSTRACT

The invention relates to ammunition for hunting guns. 
     The bullet is of the type comprising an internal shaft ( 4 ) with a rigidity equal to or greater than that of the body of the bullet, disposed in a hole drilled in the body of the bullet along its axis, and this internal shaft ( 4 ) is set back from the orifice ( 8 ) of the hole, the latter, situated on the axis, has a smaller diameter than that of the internal shaft ( 4 ), and the wall of the ogival head ( 3 ) of the bullet body ( 2 ) comprises one or more deformation notches close to the orifice of the hole. 
     Applicable to the improvement of the terminal efficiency of small, medium or large caliber hunting guns with the caliber of the gun or undersizes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to ammunition for small, medium and largecaliber guns, and more particularly to a new bullet, notably for huntingguns, having a reduced aerodynamic drag and providing an improvedterminal efficiency, in particular in a soft target.

2. Description of the Related Art

Ammunition for the most traditional hunting guns are usually sleevedbullets with a lead alloy core, whose front portion comprises an ogivewith a flattened or rounded head. According to a variant, certainbullets have a central channel in the ogive. Thus, U.S. Pat. No.3,881,421 describes a bullet whose head is hollowed out to cause it toflatten on impact with the target. This ammunition usually has thedisadvantage of a high velocity loss on the trajectory and a major lossof mass on impact with the target due to a break-up of the bullet.

Also known are bullets of the same type comprising, on the front end ofthe ogive, a part made of plastic or other materials intended to improvethe aerodynamics of the bullet and the accuracy of the shot, as inpatent CH 625043. However, these bullets fragment and expand poorly onimpact with the target, which impairs their terminal efficiency.

Application WO 0045120 describes a bullet comprising a broadened basemetal core, supporting an envelope with an open ogival head protrudingfrom the central core. U.S. Pat. No. 5,259,320 shows an example of amonometallic lead-free bullet, comprising a central channel situated inthe ogive, which has fracture notches intended to control the expansionof the head of the cone and its rolling up in petals, on impact with thetarget. This technique has the disadvantage of a random expansion, and arisk of fragmentation of the petals formed. In addition, the method ofmanufacture of this type of bullet by cold stamping causes dynamicimbalances which have the effect of a dispersion of the shots.

The technique of shafted bullet ammunition is today well known. Thisammunition comprises a sub-projectile (shaft) stabilized by fins,associated with a sabot (or launcher) having the caliber of the gun, andis described for example in patent FR-A-2.555.728. An enhancement madeto this technique is described in patent FR-A-2.795.170 relating to amonometallic bullet with the caliber of the gun or undersize, comprisingan internal shaft with a rigidity greater than that of the body of thebullet, disposed along its axis. Bullets of this type are extremelyaccurate and make it possible to regulate the expansion and retain themass of the bullet on impact with the target. According to thistechnique, the diameter of the nose of the ogive representsapproximately between 40 and 50% of the maximum diameter of the bullet,which provides it with considerable aerodynamic drag. These bullets aretherefore mainly intended for “bush-beating” shooting, over short andmedium distances, less than 150 m for rifles and of the order of 50 to60 m for shotguns. Beyond these distances, and mainly with low initialvelocity bullets, the velocity on impact with the target is too low tocause a radial expansion of the body of the bullet that is necessary forsatisfactory efficiency.

For “close range” or “stalking” shooting, it is essential to reduce theaerodynamic drag of the bullet on its trajectory, without, for all that,reducing its terminal efficiency.

The precise object of the present invention is to optimize theballistics of a metal lead-free bullet of the above type to obtain thelowest possible aerodynamic drag on the trajectory while retaining anexcellent terminal efficiency on the target while preventing losses ofmass of the metal body of the bullet at great distances which may be ofthe order of 300 m.

SUMMARY OF THE INVENTION

The subject of the present invention is therefore a bullet for a small,medium or large caliber gun, with the caliber of the gun or undersize,of the type comprising an internal shaft with a rigidity equal to orgreater than that of the body of the bullet, disposed in a hole drilledin the body of the bullet along its axis, wherein the internal shaft isset back from the orifice of the hole, the latter, situated on the axis,has a smaller diameter than that of the internal shaft, and the wall ofthe ogival head of the bullet body comprises one or more deformationnotches close to the orifice of the hole.

According to a preferred embodiment, the deformation notches of theogival head are made by a narrowing of the ogival head, separating theogival nose from the rear portion of the ogive.

Thus, the bullet of the invention has, in its front portion, a conicalor cylindro-conical shaped cavity, delimited on its large base by thefront face of the internal shaft, and opening onto the ogival nose ofthe bullet via a small orifice, preferably circular, situated in theaxis.

The ogive forming the head of the bullet is very streamlined, so as toprocure as little as possible aerodynamic drag, and for this purpose,the orifice of the hole enclosing the internal shaft has a smallerdiameter than that of the internal shaft, the ratio d₁/d of the diameterd₁ of the orifice to the diameter d of the internal shaft lying between0.1:1 and 0.9:1.

According to an advantageous embodiment of the invention, the nose ofthe ogive comprises a flat whose external diameter d₂ is such that theratio d₂/d lies between 0.3:1 and 1.5:1. According to a preferredembodiment of the invention, the ratio d₂/d lies between 0.6:1 and 1:1,while the diameter d₁ of the orifice is such that the ratio d₁/d liesbetween approximately 0.3:1 and 0.6:1.

The deformation notches made in the wall of the ogival head are intendedto make it easier for the nose of the ogive to deform and open on impactwith the target, in order to cause a deformation by “mushrooming”.

These deformation notches contribute to the stepped ogival shape of thefront portion of the bullet. This ogival shape comprises an ogival nosesurrounding the orifice communicating with the conical orcylindro-conical cavity, and a rear portion, which interact to minimizeand reduce as much as possible any discontinuity of air flow in flightwhich could cause Mach wave detachments impairing the aerodynamic drag.

As indicated above, these deformation notches may preferably be made inthe shape of a narrowing in the external wall of the ogive, separatingthe ogival nose, open to the front, from the rear portion of the ogive,so that the cross section of the base of the ogival nose is slightlygreater than that of the front of the rear portion of the ogive. Thisnarrowing is preferably situated at the base of the internal conical orcylindro-conical cavity formed in front of the internal shaft, orslightly ahead of this base, and more preferably at the line where theconical and cylindrical surfaces meet when the internal cavity is of thecylindro-conical shape.

The narrowing made in the wall of the ogive to form the deformationnotch is materialized by a crank between the base of the ogival nose andthe front end of the rear portion of the ogive, and the radial height ofthis crank, for medium caliber bullets, usually lies between 0.05 and 1mm, and preferably between 0.1 and 0.5 mm.

The theoretical profile of the ogival nose and of the rear portion ofthe ogive meet along a tangential line situated at a distance of between⅕ and ⅘ approximately, preferably between ⅓ and ⅔ approximately, of theheight of the rear portion of the ogive. Preferably, the rear portion ofthe ogive has a convex profile.

According to an advantageous embodiment of the invention, the internalcavity has a cylindro-conical shape, where the cylinder and the cone arecoaxial, joining via the large base of the cone, the latter being placedin front of the cylinder. According to a variant, the internal cavityhas a dual truncated cone shape, the two cones being joined at theirlarge base, the small base of the rear truncated cone being closed bythe internal shaft.

According to another advantageous embodiment, the front of the internalshaft protrudes slightly into the internal cavity formed in the ogivalnose, that is to say that the truncated cone-shaped or cylindrical wallof the base of the internal cavity comes into contact with the externalsurface of the shaft slightly behind the front end of the latter. Thishas the effect of forming an annular volume that may serve as anexpansion notch of the bullet head on impact with the target.

The internal shaft inserted into the body of the metal bullet may bemade of one or more elements. When it consists of a single cylindricalelement, the latter preferably supports several longitudinal ortransverse ribs that improve the connection with the bullet body. Thehole drilled in the bullet body, into which the internal shaft isinserted, may be a through or blind hole, and preferably blind.

The bullet according to the present invention has the advantage ofsubstantially reducing the aerodynamic drag on the trajectory, whileensuring control of the deformation of the body of the bullet on impactwith the target, even at great distance. Thus, by comparison with abullet according to patent FR-A-2.795.170 having the same mass and thesame dimensions, the coefficient of aerodynamic drag is reduced byapproximately half for projectile velocities of the order of Mach 2.

More particularly, the low aerodynamic drag on the trajectory allows thebullet of the invention to retain a high velocity until impact with atarget more than 300 m away. Thus, the bullet then deforms in acontrolled manner by rolling up about its axis, on impact with the softportions of the target, and ensures the effective destruction of thehard portions of said target, even at great distances, which may begreater than 300 m in the case of bullets of the caliber.

This result may be obtained, according to the invention, with a metallead-free bullet, although the volumic mass of the materials usuallyused as lead substitutes is approximately 20% less than the latter, andthe volume of the bullet is substantially identical because of thestandards imposed in this technical field. It is known that the highestpossible bullet mass is necessary, for a given caliber and a determinedaerodynamic drag coefficient, to obtain sufficient energy on impact. Theinvention therefore makes it possible to offset the consequences of thereduction in the volumic mass of lead-free bullets, and to improve theterminal efficiency of the bullet.

As indicated above, the bullet of the invention is preferably a metallead-free bullet. The body of the bullet may be made of metal or metalalloy chosen from copper and the copper alloys, and preferably a brasscontaining 5 to 40% zinc.

The shaft or metal insert in the axis of the bullet may be made of metalor metal alloy chosen from steel, copper and the aluminum or copperalloys, for example a brass.

The bullet of the invention may be manufactured by conventionaltechniques, for example by first forming a bullet provided with acylindrical axial hole opening to the front, inserting the internalshaft, and then forming the ogival nose by mechanical cold forming.

The invention applies to hunting gun bullets that are gyrostabilized orstabilized by fins, of the caliber of the gun or undersize, associatedwith a launch sabot.

The features and advantages of the present invention will appear ingreater detail in the following description, relating to preferredembodiments, with reference to the appended drawings, which represent:

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS

FIG. 1: a schematic view of a gyrostabilized bullet with the caliber ofthe gun, according to the invention.

FIG. 2: a partial view in section of the front portion of the ogive ofthe bullet of FIG. 1, showing the beginning of deformation on impactwith the target.

FIG. 3: a partial view in section of the front portion of the ogive, atthe beginning of penetration into the target after impact.

FIG. 4: a schematic half-view in partial section of a variant embodimentof the invention, representing an undersize bullet.

FIG. 5: a partial half-view in section of a variant of the internalcavity of the ogive of the bullet of FIG. 1.

FIG. 6: an external half-view of the bullet of FIG. 1 comprising acrimping groove where the ogive and the central portion of the bulletmeet.

FIG. 7: a front view of the nose of the ogive comprising thefragmentation notches of the wall.

DETAILED DESCRIPTION

As shown in FIG. 1, the bullet with the caliber of the gun is of themonobloc metal type and comprises at its rear portion a basal narrowing(1), at its central portion a body (2), and at its front portion astepped ogive (3).

An internal supported shaft (4) whose surface supports longitudinal ribs(5) is placed in a hole drilled in the axis of the bullet body andpassing through the ogive (3).

The bullet supporting the internal shaft (4) is inserted into a casefurnished with a percussion cap and a charge, of conventional type, notshown.

The ogival head (3) of the bullet is very streamlined to reduceaerodynamic drag as much as possible, and the diameters d₁ of theorifice (8) and d₂ of the flat (6) of the nose (7) that surrounds it areas small as possible. Thus, in the example of FIG. 1, the diameter d₂ ofthe flat is slightly less than the diameter d of the internal shaft (4),the ratio d₂:d being close to 0.8:1, while the diameter d₁ of theorifice is such that the ratio d₁:d is equal to approximately 0.5.

The internal cylindro-conical cavity (9) thus delimited, opens into thenose (7) of the ogive (3) via the circular shaped orifice (8).

The theoretical profile of the nose (7) and the rear portion (10) of theogive (3) meet on a tangential line situated at a distance (1) ofapproximately ½ the height of the rear portion (10) of the ogive fromthe connection of the latter with the central portion (2) of the bullet.

The large base of the nose of the stepped ogive (3) has a diameter d₄slightly greater than the front diameter d3 of the rear portion of theogive. This arrangement, in relation to the shape of the internal cavity(9) causes a thinning of the wall of the ogival head, thus generating aline of mechanical weakness (11). This line of weakness (11) makes itpossible to control the deformation of the ogival head (3) on impactwith the target.

FIG. 2 shows the beginning of the deformation of the stepped ogive (3)on impact with the target. The force (F) is exerted on the base of theflat (6) of the nose (7) of the stepped ogive (3) of the bullet. Thus,the nose (7) crumples progressively while causing a radial expansion ofthe wall of the nose, whose point of articulation is situated at rightangles to the line of mechanical weakness (11). This movement causes thedeformation by radial expansion of the front of the portion (10) of theogive (3), causing the formation of a conical entrance (12) which thengenerates the “mushrooming” of the bullet.

At the same time, the soft portions of the target are engaged in thecavity (9) and in the conical entrance (12), and they thus create aconsiderable radial pressure Pi on the internal walls of the cavity (9).This pressure, combined with the line of mechanical weakness (11)contributes to the initiation of the process of “mushrooming” or ofexpansion of the bullet.

FIG. 3 shows the evolution of the process of “mushrooming” of thebullet. The conical entrance (12) continues to open, while the ogivalhead (3) of the bullet rolls up about the axis of the bullet, uncoveringthe front point of the internal shaft (4) whose rigidity is greater thanthat of the body of the bullet. When the “mushrooming” process hasreached its end phase, the wall of the ogival head of the bullet istotally inside out and the body of the bullet then has a mushroom shapewithout loss of material, while the internal shaft may, where necessary,be detached. The diameter of the bullet body thus deformed isapproximately three times the initial diameter.

FIG. 4 represents the invention applied to an undersize bullet (13)supporting a fin (14) on its rear portion, housed in a launch sabot(15), the assembly being placed, in the usual manner, in a primed andcharged cartridge case, not shown.

As shown in FIG. 4, the stepped ogive (16) comprises a nose (17) whoselarge base has a diameter (identical to the diameter d₄ of FIG. 1)greater than the diameter of the front of the rear portion (18) of theogive (16) (identical to the diameter d₃ of FIG. 1). The internal cavity(19) is substantially identical to the internal cavity (9) of the bulletof FIG. 1, and operates in the same manner on impact with the target.

This undersize bullet may be used in a shotgun with a smooth or slightlyrifled barrel for shooting distances not usually exceeding 100 meters.This bullet is stabilized on the trajectory by the fin (14).

A variant embodiment of the ogival nose of the bullet is shown in FIG.5.

As this figure shows, the internal cavity (9) consists of two trunks ofcones joining at their large base, so that the truncated cone surface(20) of the rear portion and the truncated cone surface (21) of thefront portion meet on a line situated immediately next to the narrowingat the base of the ogival nose.

In this embodiment, the distance 11 between the plane of the orifice (8)and the line (22) where the two truncated cone surfaces (20) and (21)meet is equal to approximately 1.5 times the distance 12 separating thissame line of the plane from the line where the truncated cone surface(20) and the surface of the internal shaft (4) meet.

According to a variant (not shown), the truncated cone surface (20)meets the external surface of the internal shaft (4) slightly behind thefront end of the latter. According to another variant, the junction (22)between the two truncated cone surfaces (20) and (21) occurs on arounded surface or else, the truncated cone surface (20) is replaced bya spherical ring surface connecting without interruption to thetruncated cone surface (21).

FIG. 6 shows, in an external half-view, a variant of the bullet of FIG.1, comprising a crimping groove (23) situated on the theoreticalconnection (24) of the rear portion (10) of the ogival head with thebody (2) of the bullet. This rear portion (10) of the ogive has a convexprofile.

The crimping groove (23) here has a rectangular cross section. It isintended to make it easier to install and hold the bullet in thecartridge.

According to a conventional technique, the body (2) of the bullet maycomprise decompression grooves.

As shown in FIG. 7, the orifice (8) may have fragmentation notches (25)which make it easier to partially open the ogival nose (7) thusaccelerating the deformation of the head of the bullet on impact withthe target.

1. A bullet for a small, medium or large caliber gun, with the caliberof the bullet of the type comprising an internal shaft with a rigiditygreater than that of the body of the bullet, disposed in a blind holedrilled in the body of the bullet along its axis and which opens on thefront ogival head of the bullet, characterized in that the internalshaft is set back from the orifice of the hole, and wherein the orificeof the hole situated on the axis has a smaller diameter than that of theinternal shaft, and the wall of the ogival head of the bullet bodycomprises one or more deformation notches close to the orifice of thehole, the one or more deformation notches made by a narrowing of theogival head, which comprises a nose and a rear portion, separated by theone or more deformation notches, and a cavity of conical orcylindro-conical shape, with the cavity having a large base, which isdelimited by the front face of the internal shaft, and with a diameterof the cavity being larger than the diameter of the hole encompassingthe shaft, and with the ogival rear portion smoothly narrowing to thebase of the nose of the ogive, with the base widening to a cross-sectionslightly larger than the top of the rear portion.
 2. The bullet asclaimed in claim 1, wherein the narrowing is situated at the base of theconical or cylindro-conical internal cavity formed in front of theinternal shaft or slightly in front of this base.
 3. The bullet asclaimed in claim 2, wherein the narrowing made in the wall of the ogiveforms a deformation notch between the large base of the ogival nose andthe front end of the rear portion of the ogive, the height of thedeformation notch lying between 0.05 and 1 mm.
 4. The bullet as claimedin claim 1, wherein the internal cavity is cylindro-conical in shape andthe narrowing is situated at the line where the conical and cylindricalsurfaces meet.
 5. The bullet as claimed in claim 4, wherein thenarrowing made in the wall of the ogive forms a deformation notchbetween the large base of the ogival nose and the front end of the rearportion of the ogive, the height of the deformation notch lying between0.05 and 1 mm.
 6. The bullet as claimed in claim 1, wherein thenarrowing made in the wall of the ogive forms a deformation notchbetween the large base of the ogival nose and the front end of the rearportion of the ogive, the height of the deformation notch lying between0.05 and 1 mm.
 7. The bullet as claimed in claim 1, wherein the ratio ofthe diameter d₁ of the orifice to the diameter d of the internal shaftlies between 0.1:1 and 0.9:1.
 8. The bullet as claimed in claim 1,wherein the nose of the ogive comprises a flat nose whose externaldiameter d₂ is such that the ratio of the external diameter of the flatnose to the diameter d of the internal shaft d₂/d lies between 0.3:1 and1.5:1.
 9. The bullet as claimed in claim 8, wherein the ratio d₂/d liesbetween 0.6:1 and 1:1, while the diameter d₁ of the orifice is such thatthe ratio of the diameter of the orifice to the diameter d₁ of theinternal shaft d₁/d lies between 0.3:1 and 0.6:1.
 10. The bullet asclaimed in claim 1, wherein the narrowing is situated at the base of theconical or cylindro-conical internal cavity formed in front of theinternal shaft or slightly in front of this base.
 11. The bullet asclaimed in claim 1, wherein the internal cavity is cylindro-conical inshape and the narrowing is situated at the line where the conical andcylindrical surfaces meet.
 12. The bullet as claimed in claim 1, whereinthe narrowing made in the wall of the ogive forms a deformation notchbetween the large base of the ogival nose and the front end of the rearportion of the ogive, the height of the deformation notch lying between0.05 and 1 mm.
 13. The bullet as claimed in claim 1, wherein the nose ofthe ogive comprises a flat nose whose external diameter d₂ is such thatthe ratio of the external diameter of the flat nose to the diameter d ofthe internal shaft d₂/d lies between 0.3:1 and 1.5:1.
 14. The bullet asclaimed in claim 1, wherein the nose of the ogive comprises a flat nosewhose external diameter d₂ is such that the ratio of the externaldiameter of the flat nose to the diameter d of the internal shaft d₂/dlies between 0.3:1 and 1.5:1.
 15. The bullet as claimed in claim 1,wherein the nose of the ogive comprises a flat nose whose externaldiameter d₂ is such that the ratio of the external diameter of the flatnose to the diameter d of the internal shaft d₂/d lies between 0.3:1 and1.5:1.